I have an array of items (terms), which will be put as <option> tags in a <select>. If any of these items are in another array (termsAlreadyTaking), they should be removed first. Here is how I have done it:
// If the user has a term like "Fall 2010" already selected, we don't need that in the list of terms to add.
for (var i = 0; i < terms.length; i++)
{
for (var iAlreadyTaking = 0; iAlreadyTaking < termsAlreadyTaking.length; iAlreadyTaking++)
{
if (terms[i]['pk'] == termsAlreadyTaking[iAlreadyTaking]['pk'])
{
terms.splice(i, 1); // remove terms[i] without leaving a hole in the array
continue;
}
}
}
Is there a better way to do this? It feels a bit clumsy.
I'm using jQuery, if it makes a difference.
UPDATE Based on #Matthew Flaschen's answer:
// If the user has a term like "Fall 2010" already selected, we don't need that in the list of terms to add.
var options_for_selector = $.grep(all_possible_choices, function(elem)
{
var already_chosen = false;
$.each(response_chosen_items, function(index, chosen_elem)
{
if (chosen_elem['pk'] == elem['pk'])
{
already_chosen = true;
return;
}
});
return ! already_chosen;
});
The reason it gets a bit more verbose in the middle is that $.inArray() is returning false, because the duplicates I'm looking for don't strictly equal one another in the == sense. However, all their values are the same. Can I make this more concise?
var terms = $.grep(terms, function(el)
{
return $.inArray(el, termsAlreadyTaking) == -1;
});
This still has m * n performance (m and n are the lengths of the arrays), but it shouldn't be a big deal as long as they're relatively small. To get m + n, you could use a hashtable
Note that ECMAScript provides the similar Array.filter and Array.indexOf. However, they're not implemented in all browsers yet, so you would have to use the MDC implementations as a fallback. Since you're using jQuery, grep and inArray (which uses native indexOf when available) are easier.
EDIT:
You could do:
var response_chosen_pk = $.map(response_chosen_items, function(elem)
{
return elem.pk;
});
var options_for_selector = $.grep(all_possible_choices, function(elem)
{
return $.inArray(elem.pk, response_chosen_pk) == -1;
});
http://github.com/danstocker/jorder
Create a jOrder table on termsAlreadyTaking, and index it with pk.
var table = jOrder(termsAlreadyTaking)
.index('pk', ['pk']);
Then you can search a lot faster:
...
if ([] == table.where([{ pk: terms[i].pk }]))
{
...
}
...
Related
I have search through quite a lot of questions here, but havent found one that i think fits my bill, so if you know of one please link to it.
I have an array that i want to search through for a specific number and if that number is in the array, i then want to take an action and if not then another action.
I have something like this
var Array = ["1","8","17","14","11","20","2","6"];
for(x=0;x<=Array.length;x++)
{
if(Array[x]==8)
then change picture.src to srcpicture1
else
then change picture.src to srcpicture2
}
but this will run the lenght of the array and end up checking the last element of the array and since the last element is not 8 then it will change the picture to picture2.
Now i can see why this happens, i just dont have any ideas as to how to go about checking if an array contains a specific number.
Thanks in advance.
What you can do is write yourself a function to check if an element belongs to an array:
function inArray(array, value) {
for (var i = 0; i < array.length; i++) {
if (array[i] == value) return true;
}
return false;
}
And the just do:
var arr = ["1","8","17","14","11","20","2","6"];
if (inArray(arr, 8)) {
// change picture.src to srcpicture1
} else {
// change picture.src to srcpicture2
}
It's a lot more readable to me.
For extra points you can add the function to the array prototype like so:
Array.prototype.has = function (value) {
for (var i = 0; i < this.length; i++) {
if (this[i] === value) return true;
}
return false;
};
And then the call would be
if (arr.has(8)) // ...
Pushing this even further, you can check for indexOf() method on array and use it - if not - replace it with the code above.
P.S. Try not to use Array for a variable name, since it's reserved for the actual array type.
use this
http://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf
ie version
https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf#Compatibility
Why don't just you abort the loop when you find the right number :
for(x=0;x<=Array.length;x++)
{
if(Array[x]==8) {
//change picture.src to srcpicture1
break;
}
}
You could sort the array first then check the array only up to the point at which a number would be in the array, were it to exist.
If you have unique keys and a faster retrieval is what you care about a lot, you can consider using a map instead of an array (if there's a hard-bound case of using an array, then it won't work of course). If using a map, you just check "if( num in arr ) ".
I have an array of characters like this:
['a','b','c','d','f']
['O','Q','R','S']
If we see that, there is one letter is missing from each of the arrays. First one has e missing and the second one has P missing. Care to be taken for the case of the character as well. So, if I have a huge Object which has all the letters in order, and check them for the next ones, and compare?
I am totally confused on what approach to follow! This is what I have got till now:
var chars = ("abcdefghijklmnopqrstuvwxyz"+"abcdefghijklmnopqrstuvwxyz".toUpperCase()).split("");
So this gives me with:
["a","b","c","d","e","f","g","h","i","j","k","l","m",
"n","o","p","q","r","s","t","u","v","w","x","y","z",
"A","B","C","D","E","F","G","H","I","J","K","L","M",
"N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
Which is awesome. Now my question is, how do I like check for the missing character in the range? Some kind of forward lookup?
I tried something like this:
Find the indexOf starting value in the source array.
Compare it with each of them.
If the comparison failed, return the one from the original array?
I think that a much better way is to check for each element in your array if the next element is the next char:
function checkMissingChar(ar) {
for (var i = 1; i < ar.length; i++) {
if (ar[i].charCodeAt(0) == ar[i-1].charCodeAt(0)+1) {
// console.log('all good');
} else {
return String.fromCharCode(ar[i-1].charCodeAt(0)+1);
}
}
return true;
}
var a = ['a','b','c','d','f']
var b = ['O','Q','R','S']
console.log(checkMissingChar(a));
console.log(checkMissingChar(b));
Not that I start to check the array with the second item because I compare it to the item before (the first in the Array).
Forward Look-Ahead or Negative Look-Ahead: Well, my solution would be some kind of that. So, if you see this, what I would do is, I'll keep track of them using the Character's Code using charCodeAt, instead of the array.
function findMissingLetter(array) {
var ords = array.map(function (v) {
return v.charCodeAt(0);
});
var prevOrd = "p";
for (var i = 0; i < ords.length; i++) {
if (prevOrd == "p") {
prevOrd = ords[i];
continue;
}
if (prevOrd + 1 != ords[i]) {
return String.fromCharCode(ords[i] - 1);
}
prevOrd = ords[i];
}
}
console.log(findMissingLetter(['a','b','c','d','f']));
console.log(findMissingLetter(['O','Q','R','S']));
Since I come from a PHP background, I use some PHP related terms like ordinal, etc. In PHP, you can get the charCode using the ord().
As Dekel's answer is better than mine, I'll try to propose somewhat more better answer:
function findMissingLetter (ar) {
for (var i = 1; i < ar.length; i++) {
if (ar[i].charCodeAt(0) != ar[i-1].charCodeAt(0)+1) {
return String.fromCharCode(ar[i-1].charCodeAt(0)+1);
}
}
return true;
}
var a = ['a','b','c','d','f']
var b = ['O','Q','R','S']
console.log(findMissingLetter(a));
console.log(findMissingLetter(b));
Shorter and Sweet.
I'm very new to JS so go easy on me. I've got this array inside a variable, and am trying to find a better way to write that if statement. So if the names inside that variable grow, I won't need to change the if statement as it won't be hardcoded.
var names = ["beth", "barry", "debbie", "peter"]
if (names[0] && names [1] && names [2] && names [3] {
Do something...
}
Something tells me I need to be using the .length property but I can't work out how to properly use it within that statement. Something along the lines of:
if (names[i] * names.length) {
Do something...
}
I know that's wrong. I think need to be finding the index of each and looping through it makign sure it the loop doesn't exceed the amount of values in the array.
Any help is appreciated. Thanks in advance!
Update: Some users have alerted me that my question might not be as clear. I've setup a CodePen here (http://codepen.io/realph/pen/KjCLd?editors=101) that might explain what I'm trying to achieve.
P.S. How do I stop my from repeating 3 times?
You can use every to test whether every element satisfies some condition:
if (names.every(function (name) { return name })) {
// Do Something
}
every will automatically stop testing when the first non-true element is found, which is potentially a large optimization depending on the size of your array.
Traditionally, you would simply iterate over the array and test each element. You can do so with forEach or a simple for loop. You can perform the same early-termination when you find a non-true element by returning false from the forEach callback.
var allTrue = true;
names.forEach(function (name) {
return allTrue = allTrue && name;
});
if (allTrue) {
// Do something...
}
Please give a english description of what you are trying to accomplish. The below answer assumes you simply want to iterate a list of names and do some processing with each.
You want to use a for loop.
var names = ["beth", "barry", "debbie", "peter"]
for (var i=0; i<names.length; i++) {
// access names[i]
}
The best cross-browser solution is to use a traditional for loop.
var names = ["beth", "barry", "debbie", "peter"],
isValid = true,
i;
for (i = 0; i < names.length; i++) {
isValid = isValid && names[i];
}
if (isValid) {
// do something
}
You can try this;
var checkCondition = true;
for(var i = 0; i<names.length; i++){
if(names[i] !== something) {
checkCondition = false;
break;
}
}
if(checkCondition){
//Do what ever you like if the condition holds
}else{
// Do whatever you like if the condition does NOT holds
}
If i understand right you need something like this
var names = ["beth", "barry", "debbie", "peter"];
var notUndefinedNames = names.filter(function(el){return el !== undefined;});
// if all
if (names.length === notUndefinedNames.length) console.log("You're all here. Great! Sit down and let's begin the class.");
// if one or less
else if (notUndefinedNames.length <= 1) console.log("I can't teach just one person. Class is cancelled.");
else console.log("Welcome " + notUndefinedNames.join(', '));
There's a gap in my JavaScript knowledge here. I want to search an array of objects values for a particular value and return it.
For the year I have been writing JavaScript, I have been implementing it like this:
var itemClicked = (function(){
var retval;
//Note self.inventory.itemsArray is an array of JS objects
$(self.inventory.itemsArray).each(function(i){
if(parseInt(this.id) === parseInt(idOfItem)){
retval = this;
return false;
}
});
return retval;
})();
It works, but I'm sure as anything there is a more elegant way. Tell me please!
EDIT - Solution
Thanks to #gdoron with his answer below.
var myVar = $(self.owner.itemsArray).filter(function(){
return parseInt(this.id) == parseInt(recItemID);
}).get(0);
Note: .get(0) was added at the end because myVar is wrapped as a jQuery object.
The native jQuery function for this is filter:
$(data).filter(function(){
return this.id == "foo";
});
It's shorter than code you have and more important a lot more readable.
About efficiency, it will iterate all the elements in the set to find as much as possible matches, but I hardly believe it will be the bottle neck of your application, don't focus on micro-optimisations.
I suggest you read Eric Lipper blog about Which is faster.
You can also use grep as suggested by #Mattias Buelens:
$.grep(data, function(ele){
retun ele.id == "foo";
});
Just another option using jQuery's $.grep( ) function
var arr = $.grep( self.inventory.itemsArray, function ( n ) {
return n.id == idOfItem;
});
The above returns an array of matching array elements. If you just want the first it is easy enough to return arr[0] if it exists.
Although I'm unsure what the function is actually supposed to do (due to the external contexts' variables), the following should be more efficient cycle-wise
var itemClicked = (function(){
var i, array = self.inventory.itemsArray, length = array.length;
for( i=0; i < length; i++) {
if(parseInt(array[i].id) === parseInt(idOfItem)){
return array[i];
}
}
return undefined;
})();
It's an array of Javascript objects
Then do not use jQuery at all. At least, use $.each instead of building a wrapper object around the array. Still, a simple for-loop is much shorter and more performant:
var itemClicked = (function(idnum) {
var arr = self.inventory.itemsArray;
for (var i=0, l=arr.length; i<l; i++)
if (parseInt(arr[i].id, 10) === idnum)
return arr[i];
})( parseInt(idOfItem, 10) );
You might as well think of storing the id properties as numbers right away, so you don't need to convert it each time.
My data[l][m] contains 1,2,3,4,5
I'm trying to search for a particular number, say '2' in it. Is there a better way to do this?
for (var n = 0; n < data[l][m].length; n++) {
if(data[l][m][n] == num){ // num is equal to '2'
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
}
And how about in: ['id1',['a',[1,2,3,4,5]],['b',[3,4,5,6,7]]]
Many thanks in advance.
If you're already including jQuery, use $.inArray(), like this:
if($.inArray(num, data[l][m]) > -1) {
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
The shorter vanilla JS version is a direct .indexOf() on the Array, but IE doesn't have this by default.
You could use indexOf, although it still has the same O(n) complexity as your for loop:
var pos = data[l][m].indexOf(num);
if (pos !== -1)
{
// element was found
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
Note, however, that older versions of IE do not have the indexOf method for Arrays.
I have no major changes to recommend, but do have a couple tweaks to suggest. The first is to create a temporary reference to data[l] to reduce reading complexity by 1 level. This is a cosmetic change for the benefit of the coder. The other is cache the length of the array you are searching, which helps with performance. If you replace your for loop with the while loop as follows, you can also remove the comparison operations.
var layer1 = data[l];
var n = layer1[m].length;
while (n--) {
if (layer1[m][n] == num) { // num is equal to '2'
number = layer1[0];
document.form.options[l - 1] = new Option(number, number, true, true);
}
}